1. Field of the Invention
The invention relates to surveying and/or altering the topography of a worksite, and more particularly, to an apparatus and method for creating, updating and displaying a surface model of the worksite in real-time.
2. Background Information
Throughout this application, various publications, patents and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure.
Relatively sophisticated and powerful geography altering or earth-moving machinery have been developed to recontour the topography of large plots of land, or to otherwise alter the geography of a worksite such as a construction area, mine, road and the like. Such operations often involve the necessity of a survey to obtain the coordinates of a large number of points over the worksite and to thereafter construct a three-dimensional model of the site. From the survey an architectural plan or target geography is developed. Thereafter, survey stakes are placed on the site marked with information or colored to provide physical cues to the operator of the geography altering machinery as to how the machine should be operated to transform the worksite from the original to the desired state. Often, the survey operations are carried out manually, using line of sight optical instruments or other static, point-by-point measuring techniques to obtain the coordinates of the worksite. In this event, a relatively great deal of skill and experience on the part of the operator of the earth moving equipment is required to recontour a large landsite, due in part to the absence of large scale as well as detailed information of the progress being made during the revision of the site.
As a result, most projects involving alteration of the geography of large worksites are generally time consuming and labor intensive due to the requirements for skilled personnel and large crews to direct the operation of earth moving machinery and the like.
In addition, the operation is often interrupted while a survey crew verifies the amount of progress to date and manually updates the staking and marking of the site, as well as the site model.
In efforts to improve the efficiency of such earth moving operations, several methods and systems utilizing satellite-based navigational systems such as the United States Global Positioning System (GPS) or the Russian Global Orbiting Navigation Satellite System (GLONASS), have been devised.
For example, U.S. Pat. No. 4,807,131 to Clegg discloses the concept of utilizing GPS to determine the position of an earth-engaging blade of earth moving equipment. The slope or angle of the blade is then determined, followed by inputting the desired soil topography into a computer. This data is then utilized to adjust the position and slope of the blade to achieve the desired soil topography.
U.S. Pat. No. 5,375,663 to Teach discloses an earth moving apparatus and method for grading a tract of land. This concept includes determination of blade elevation (z-coordinate), such as with a laser system. The distance between the blade and the soil elevation is determined with suitable sensors, such as with an ultrasonic device or system. This data, along with horizontal (x and y) coordinates obtained from GPS or other systems, and with data regarding desired soil topography, are combined to determine the distance between actual and desired soil elevation.
U.S. Pat. No. 5,631,658 to Gudat et al. discloses a similar concept for operating geography-altering machinery relative to a worksite. This concept generally includes determining the three dimensional (x, y, z coordinate) position of a portion of the machinery, such as by utilizing GPS. The position of the equipment is recorded as the equipment is operated, and utilized to determine a path of the machine in real time. This path is then compared to the desired soil topography using a computer to derive the distance between the actual soil topography and the desired soil topography in real time.
The above-referenced concepts have various drawbacks which generally limit their usefulness in various applications. For example, Clegg and Teach each determine blade position and utilize additional sensors to determine the distance between the blade and the soil. This approach ends to be relatively complex. Such complexity may adversely affect system reliability and/or accuracy.
The Gudat reference also disadvantageously discloses a relatively complicated system for generating the path of the earth moving machinery in real time, by interpolating between position data points, ostensibly to improve the accuracy of its soil topography calculations. Such complexity, however, disadvantageously tends to increase the processing time required to run the software, to slow system operation and/or necessitate the use of relatively sophisticated and expensive computer hardware and/or software.
Moreover, none of the above-referenced patents appear to have recognized or addressed the problem of inaccuracies introduced due to tilting of the earth moving apparatus during operation.
For example, an important problem associated with prior art systems is that the height of the GPS antenna on a bulldozer or inspection vehicle may be 16 feet or more above the earth surface and, when the vehicle is tilted to a significant degree such as on a 20.degree. slope, the position calculated using the GPS signal may be in error by about 1 foot (0.3 m) or more in height and about 5.5 feet (1.7 m) in the horizontal plane. This tends to negate the accuracy advantage of utilizing the GPS system which can typically determine the three-dimensional location of the signal-receiving portion of the GPS antenna to within 3 centimeters. With tilt in any direction, the actual distance in the vertical (z-direction) from the GPS signal-receiving antenna portion to the point on the earth's surface will be less than the specified non-tilted distance, and thus the actual elevation of the ground point will be higher than the z-coordinate calculated using the GPS signal. Also, as mentioned above, the actual x and/or y coordinates (position in the horizontal plane) of the point will be different from the x and/or y coordinates determined directly from the GPS signal, adding further inaccuracies to the calculated position.
Thus, a need exists for an improved method and apparatus for operating geography-altering machinery which operates in a relatively simplified manner, while providing improved accuracy by tilt correction.